Stefan Jakobs

Laser Beam Submerged Arc Hybrid Welding

The laser beam-submerged arc hybrid welding method originates from the knowledge that, with increasing penetration depth, the laser beam process has a tendency to pore formation in the lower weld regions. The coupling with the energy-efficient submerged-arc process improves degassing and reduces the tendency to pore formation. The high deposition rate of the SA process in combination with the laser beam process offers, providing the appropriate choice of weld preparation, the possibility of welding plates with a thickness larger than 20° mm in a single pass, and also of welding thicker plates with the double-sided single pass technique.

Ion-assisted deposition processes: industrial network IntIon

The presented work is embedded in the research network “Integrative Ion Processes for Modern Optics”, called IntIon, consisting of 12 partners from the German optics industry and two research institutes. The main target of the IntIon network is the development of new process concepts on the basis of ion assisted deposition (IAD) for the industrial production of optical thin film components. Besides an improvement in efficiency, a major aim is concentrated on the optical characteristics for selected application fields with high economical potential. In this network, different ion and plasma sources are compared with regard to their qualification for ion assisted deposition processes. This work includes the characterization of the ion energy and ion current using Faraday-cup measurements. The selection of investigated coating materials includes a broad variety of standard and non-standard oxides. First results of the network will be presented for adapted deposition materials and different operation characteristics of ion sources.

Laser beam welding under vacuum of high grade materials

Currently, three welding processes are used in the manufacturing of large scale work pieces with high weld seam depths. The gas metal arc welding and the submerged arc welding processes are characterized by a comparatively low penetration depth and welding speed, the use of welding consumables and a high energy input per length. Electron beam welding is suitable for single pass welding of high wall thicknesses, but a fine vacuum is needed, x-ray radiation is generated, the process is prone to magnetic fields, and the technology has to face a low market penetration. Laser beam welding under vacuum (“LaVa”) is on its way to become a new and superb option for these welding tasks. The paper at hand presents the latest results of a research project which targets the qualification of LaVa for the welding of heavy-walled steel structures made of unalloyed steel or duplex stainless steel. The achieved results demonstrate that, in comparison to laser beam welding at atmospheric pressure, an increase of the penetration depth and a high process stability can be achieved, whereby economic advantages and a high weld seam quality are realized. On the other hand, the latest results of the application of LaVa for the welding of nickel-base alloys, copper, and titanium are presented. It is shown that LaVa is suitable for the welding of these materials. A high process stability is achieved; spattering is minimized; and high penetration depths are achieved.

Design and manufacturing of high-performance notch filters

Rugate designs for the realization of notch filters are well known in the literature. The required deposition of gradient index layers is difficult to manufacture. In our approach we apply the equivalent index theory to replace the gradient index profile of a notch filter design. We produce single and multiple notch filters with plasma ion-assisted deposition and broad-band optical monitoring. As examples, a 500nm notch filter for the GREGOR telescope and a 589nm notch filter for the GALACSI instrument of the VLT are discussed. Additionally, a 4-line multiple notch filter and a 218nm notch filter made for fluorescence spectroscopy applications are presented.

Laser beam welding in vacuum of thick plate structural steel

Laser beam and electron beam welding methods are well established in the manufacturing industry. Each of the methods has specific advantages which are used for a large variety of application cases.For some time now, laser beam welding in vacuum has experienced a renaissance. First tests about the topic were made in Japan as early as in the Eighties. The brilliant solid-state laser beam sources available today offer many advantages compared to the previously used CO2 laser beam sources. Higher power and beam quality is available, the interface for getting the laser into the vacuum can be designed simpler and the welding heads have a compact design. Compared with electron beam welding, laser beam welding in large vacuum chambers can be carried out with simpler means.This article covers a spotlight on the main aspects of lower pressure on the laser beam welding process and the specific advantages of laser beam welding in vacuum. Moreover it shows the recent progress made from the early phenomenological examination of the process variation to the use as welding process for connection welds on thick plate steel up to (and over) 70mm wall thickness.Laser beam and electron beam welding methods are well established in the manufacturing industry. Each of the methods has specific advantages which are used for a large variety of application cases.For some time now, laser beam welding in vacuum has experienced a renaissance. First tests about the topic were made in Japan as early as in the Eighties. The brilliant solid-state laser beam sources available today offer many advantages compared to the previously used CO2 laser beam sources. Higher power and beam quality is available, the interface for getting the laser into the vacuum can be designed simpler and the welding heads have a compact design. Compared with electron beam welding, laser beam welding in large vacuum chambers can be carried out with simpler means.This article covers a spotlight on the main aspects of lower pressure on the laser beam welding process and the specific advantages of laser beam welding in vacuum. Moreover it shows the recent progress made from the early phenomenological exami...

Advanced dielectric coatings for the Euclid mission telescope manufactured by the PARMS process

The extraordinary specification for the dichroic beamsplitter inside the Euclid telescope requires very complex coatings. Design issues considering the several boundary conditions are discussed and results from the current development are presented.

High-precision longpass filter arrays for miniature spectrometers

Arrays of longpass filter coatings for high order suppression in miniature spectrometers were produced by plasma-ion assisted deposition and photolithogaphy. The filter edges were imaged by optical microscopy, scanning electron microscopy, and scanning force microscopy. Whereas a positioning accuracy of about 2 microns was achieved, the width of the filter edges varied between 2 and 10 microns.

Consideration of surface roughness affecting the blocking depth of dielectric coatings

Reduced optical density of dielectric broad blocking filters can be attributed to substrate surface properties. Applying the model of small-scale roughness by interface overlayers, the suitability of given substrate polishing quality can be assessed.

Tailored Nanocomposite Coatings for Optics

Material mixtures offer new possibilities of synthesizing coating materials with tailored optical and mechanical properties. We present experimental results on mixtures of HfO2, ZrO2, and Al2O3pursuing applications in UV coating technology.

Analytical design of multicycle broadband AR coatings

Normal-incidence multicycle broadband AR coatings on glass with low residual over the wavelength region 400 nm to 800 nm are theoretically discussed. Using the method of effective interfaces and the concept of equivalent index layers a 4-layer design sub(AHBL)air is expanded into the designs sub[AH(C2LC)2BL]air where A, B, C, H, and L are quarter-wave layers with refractive indices nH equals 1.38, nL equals 2.35, and nL < n(Lambda ), bB, nC, < nH. These designs represent 1-cycle, 2- cycle, and 3-cycle broadband AR coatings and perform a residual reflectance of 0.20 percent, 0.14 percent, and 0.10 percent, respectively. Four other designs demonstrate the approach at other wavelength regions. In one example, all quarter-wave layers with refractive indices in-between nL and nH are analytically substituted using equivalent index layers to get two-material multilayers suitable for practical applications. After this, the design is refined with respect to the optical thickness whereby the layer number is fixed. The resulting design consists of 18 layers and performs an average residual reflectance 0.085 percent over the region 400 nm to 800 nm.